Clip

A clip step trims each input feature to the parts that fall inside a clip polygon. Features entirely outside drop out; features that cross the polygon boundary are cut.

This is the spatial "intersect with this shape" operation. Cookie-cutter: hand it a parcel layer and a city boundary, get back the parcels inside the city, with parcels on the edge trimmed at the boundary.

Inputs

• Source layer. Any geometry type (points, lines, or polygons).
• Clip layer. Another data layer you can read. Prefer a polygon layer as the cookie-cutter. The portal unions that layer's geometries and intersects the source against the result. Geo-boundary items and pasted GeoJSON are not a separate clip input on this path; put the mask in a data layer first.

Output

A new layer with the source's schema. Each row's geometry is ST_Intersection(source.geometry, clip). Rows whose geometry doesn't intersect the clip drop out entirely; rows whose geometry is entirely inside come through unchanged.

How to use it on its own

From Analyze (guided)

1. Open a data layer and switch to the Analyze tab.
2. Click Clip this layer.
3. Pick the cookie-cutter data layer.
4. Click Create derived layer.

That posts a single-step clip recipe to the portal. The job runs on PostGIS on the server. Expect a short server job, not an instant browser result. Not gated on the optional server-heavy analysis tier.

From the new-item wizard

1. New-item wizard → Derived layer.
2. Pick a Source.
3. Add a Clip step.
4. Pick the other data layer.
5. Save.

Example

You have a state-wide road network. You want just the segments inside one county. Add a Clip step with the county's geo boundary as the clip polygon. Output is the road segments trimmed to the county line.

Clip vs. spatial join with "within"

• Clip trims geometry; the output's geometry is the intersected piece. Roads sticking out beyond the county line are cut at the line.
• Spatial join with within keeps the whole input geometry if any part is inside the join polygon. Same roads, kept whole if they're "in" the county at all.

Pick clip when the geometry needs to stay within the polygon; pick spatial-join-with-within when you want intact features plus an attribute identifying which polygon they're in.

Notes

• Clip a polygon by a polygon produces a polygon. Common case for "limit this layer to the project area".
• Clip a line by a polygon produces line segments at the boundary cut.
• Clip a point by a polygon is equivalent to a filter "points inside this polygon"; same result, both work.
• The clip polygon's coordinate system is reconciled automatically.